/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.http.server.reactive;

import org.apache.commons.logging.Log;
import org.reactivestreams.Subscriber;
import org.reactivestreams.Subscription;
import org.springframework.core.io.buffer.DataBufferFactory;
import org.springframework.core.io.buffer.DefaultDataBufferFactory;
import org.springframework.http.HttpLogging;
import org.springframework.http.HttpMethod;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

import javax.servlet.AsyncContext;
import javax.servlet.AsyncEvent;
import javax.servlet.AsyncListener;
import javax.servlet.DispatcherType;
import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRegistration;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.net.URISyntaxException;
import java.util.Collection;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * Adapt {@link HttpHandler} to an {@link HttpServlet} using Servlet Async support
 * and Servlet 3.1 non-blocking I/O.
 *
 * @author Arjen Poutsma
 * @author Rossen Stoyanchev
 * @see org.springframework.web.server.adapter.AbstractReactiveWebInitializer
 * @since 5.0
 */
@SuppressWarnings("serial")
public class ServletHttpHandlerAdapter implements Servlet {

    private static final Log logger = HttpLogging.forLogName(ServletHttpHandlerAdapter.class);

    private static final int DEFAULT_BUFFER_SIZE = 8192;

    private static final String WRITE_ERROR_ATTRIBUTE_NAME = ServletHttpHandlerAdapter.class.getName() + ".ERROR";


    private final HttpHandler httpHandler;

    private int bufferSize = DEFAULT_BUFFER_SIZE;

    @Nullable
    private String servletPath;

    private DataBufferFactory dataBufferFactory = new DefaultDataBufferFactory(false);


    public ServletHttpHandlerAdapter(HttpHandler httpHandler) {
        Assert.notNull(httpHandler, "HttpHandler must not be null");
        this.httpHandler = httpHandler;
    }

    /**
     * We cannot combine ERROR_LISTENER and HandlerResultSubscriber due to:
     * https://issues.jboss.org/browse/WFLY-8515.
     */
    private static void runIfAsyncNotComplete(AsyncContext asyncContext, AtomicBoolean isCompleted, Runnable task) {
        try {
            if (asyncContext.getRequest().isAsyncStarted() && isCompleted.compareAndSet(false, true)) {
                task.run();
            }
        } catch (IllegalStateException ex) {
            // Ignore: AsyncContext recycled and should not be used
            // e.g. TIMEOUT_LISTENER (above) may have completed the AsyncContext
        }
    }

    /**
     * Return the configured input buffer size.
     */
    public int getBufferSize() {
        return this.bufferSize;
    }

    /**
     * Set the size of the input buffer used for reading in bytes.
     * <p>By default this is set to 8192.
     */
    public void setBufferSize(int bufferSize) {
        Assert.isTrue(bufferSize > 0, "Buffer size must be larger than zero");
        this.bufferSize = bufferSize;
    }

    /**
     * Return the Servlet path under which the Servlet is deployed by checking
     * the Servlet registration from {@link #init(ServletConfig)}.
     *
     * @return the path, or an empty string if the Servlet is deployed without
     * a prefix (i.e. "/" or "/*"), or {@code null} if this method is invoked
     * before the {@link #init(ServletConfig)} Servlet container callback.
     */
    @Nullable
    public String getServletPath() {
        return this.servletPath;
    }

    public DataBufferFactory getDataBufferFactory() {
        return this.dataBufferFactory;
    }


    // Servlet methods...

    public void setDataBufferFactory(DataBufferFactory dataBufferFactory) {
        Assert.notNull(dataBufferFactory, "DataBufferFactory must not be null");
        this.dataBufferFactory = dataBufferFactory;
    }

    @Override
    public void init(ServletConfig config) {
        this.servletPath = getServletPath(config);
    }

    private String getServletPath(ServletConfig config) {
        String name = config.getServletName();
        ServletRegistration registration = config.getServletContext().getServletRegistration(name);
        if (registration == null) {
            throw new IllegalStateException("ServletRegistration not found for Servlet '" + name + "'");
        }

        Collection<String> mappings = registration.getMappings();
        if (mappings.size() == 1) {
            String mapping = mappings.iterator().next();
            if (mapping.equals("/")) {
                return "";
            }
            if (mapping.endsWith("/*")) {
                String path = mapping.substring(0, mapping.length() - 2);
                if (!path.isEmpty() && logger.isDebugEnabled()) {
                    logger.debug("Found servlet mapping prefix '" + path + "' for '" + name + "'");
                }
                return path;
            }
        }

        throw new IllegalArgumentException("Expected a single Servlet mapping: " +
                "either the default Servlet mapping (i.e. '/'), " +
                "or a path based mapping (e.g. '/*', '/foo/*'). " +
                "Actual mappings: " + mappings + " for Servlet '" + name + "'");
    }

    @Override
    public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException {
        // Check for existing error attribute first
        if (DispatcherType.ASYNC.equals(request.getDispatcherType())) {
            Throwable ex = (Throwable) request.getAttribute(WRITE_ERROR_ATTRIBUTE_NAME);
            throw new ServletException("Failed to create response content", ex);
        }

        // Start async before Read/WriteListener registration
        AsyncContext asyncContext = request.startAsync();
        asyncContext.setTimeout(-1);

        ServletServerHttpRequest httpRequest;
        try {
            httpRequest = createRequest(((HttpServletRequest) request), asyncContext);
        } catch (URISyntaxException ex) {
            if (logger.isDebugEnabled()) {
                logger.debug("Failed to get request  URL: " + ex.getMessage());
            }
            ((HttpServletResponse) response).setStatus(400);
            asyncContext.complete();
            return;
        }

        ServerHttpResponse httpResponse = createResponse(((HttpServletResponse) response), asyncContext, httpRequest);
        if (httpRequest.getMethod() == HttpMethod.HEAD) {
            httpResponse = new HttpHeadResponseDecorator(httpResponse);
        }

        AtomicBoolean isCompleted = new AtomicBoolean();
        HandlerResultAsyncListener listener = new HandlerResultAsyncListener(isCompleted, httpRequest);
        asyncContext.addListener(listener);

        HandlerResultSubscriber subscriber = new HandlerResultSubscriber(asyncContext, isCompleted, httpRequest);
        this.httpHandler.handle(httpRequest, httpResponse).subscribe(subscriber);
    }

    protected ServletServerHttpRequest createRequest(HttpServletRequest request, AsyncContext context)
            throws IOException, URISyntaxException {

        Assert.notNull(this.servletPath, "Servlet path is not initialized");
        return new ServletServerHttpRequest(
                request, context, this.servletPath, getDataBufferFactory(), getBufferSize());
    }

    protected ServletServerHttpResponse createResponse(HttpServletResponse response,
                                                       AsyncContext context, ServletServerHttpRequest request) throws IOException {

        return new ServletServerHttpResponse(response, context, getDataBufferFactory(), getBufferSize(), request);
    }

    @Override
    public String getServletInfo() {
        return "";
    }

    @Override
    @Nullable
    public ServletConfig getServletConfig() {
        return null;
    }

    @Override
    public void destroy() {
    }

    private static class HandlerResultAsyncListener implements AsyncListener {

        private final AtomicBoolean isCompleted;

        private final String logPrefix;

        public HandlerResultAsyncListener(AtomicBoolean isCompleted, ServletServerHttpRequest httpRequest) {
            this.isCompleted = isCompleted;
            this.logPrefix = httpRequest.getLogPrefix();
        }

        @Override
        public void onTimeout(AsyncEvent event) {
            logger.debug(this.logPrefix + "Timeout notification");
            AsyncContext context = event.getAsyncContext();
            runIfAsyncNotComplete(context, this.isCompleted, context::complete);
        }

        @Override
        public void onError(AsyncEvent event) {
            Throwable ex = event.getThrowable();
            logger.debug(this.logPrefix + "Error notification: " + (ex != null ? ex : "<no Throwable>"));
            AsyncContext context = event.getAsyncContext();
            runIfAsyncNotComplete(context, this.isCompleted, context::complete);
        }

        @Override
        public void onStartAsync(AsyncEvent event) {
            // no-op
        }

        @Override
        public void onComplete(AsyncEvent event) {
            // no-op
        }
    }


    private class HandlerResultSubscriber implements Subscriber<Void> {

        private final AsyncContext asyncContext;

        private final AtomicBoolean isCompleted;

        private final String logPrefix;

        public HandlerResultSubscriber(
                AsyncContext asyncContext, AtomicBoolean isCompleted, ServletServerHttpRequest httpRequest) {

            this.asyncContext = asyncContext;
            this.isCompleted = isCompleted;
            this.logPrefix = httpRequest.getLogPrefix();
        }

        @Override
        public void onSubscribe(Subscription subscription) {
            subscription.request(Long.MAX_VALUE);
        }

        @Override
        public void onNext(Void aVoid) {
            // no-op
        }

        @Override
        public void onError(Throwable ex) {
            logger.trace(this.logPrefix + "Failed to complete: " + ex.getMessage());
            runIfAsyncNotComplete(this.asyncContext, this.isCompleted, () -> {
                if (this.asyncContext.getResponse().isCommitted()) {
                    logger.trace(this.logPrefix + "Dispatch to container, to raise the error on servlet thread");
                    this.asyncContext.getRequest().setAttribute(WRITE_ERROR_ATTRIBUTE_NAME, ex);
                    this.asyncContext.dispatch();
                } else {
                    try {
                        logger.trace(this.logPrefix + "Setting ServletResponse status to 500 Server Error");
                        this.asyncContext.getResponse().resetBuffer();
                        ((HttpServletResponse) this.asyncContext.getResponse()).setStatus(500);
                    } finally {
                        this.asyncContext.complete();
                    }
                }
            });
        }

        @Override
        public void onComplete() {
            logger.trace(this.logPrefix + "Handling completed");
            runIfAsyncNotComplete(this.asyncContext, this.isCompleted, this.asyncContext::complete);
        }
    }

}
